The synthesis and chemical and structural characterization of representative examples of a totally new class of compounds is proposed. The new complexes can be described as heteropoly molybdate or tungstate anions to which are attached one or more organic groups. Two of the most promising routes to such complexes are: (1) incorporation of RnXO4-nP-hetero groups (e.g., alkyl phosphonates) into new types of polyanions; (2) derivativization of known polyanions via alkylation or condensation reactions. Several examples of new molybdate complexes have already been isolated and characterized by our group within the past year. The main thrust of the proposed research is the characterization of relatively large (6-15 A) polytungstate derivatives with functionalized organic groups that are hydrolytically stable at pH 5-8. Following synthesis and chemical analysis, the chemical properties and structures of the new complexes will be determined by spectroscopic, electrochemical and X-ray crystallographic methods. The long term goal of this research is to explore the use of such heavy metal complexes in labelling molecules of biological interest. Applications as highly specific electron microscopic stains, X-ray "heavy atom" labels, biopolymer charge and mass modifiers, and NMR shift reagents are described.